1. Field of the Invention
The present invention relates to a contact (a probe) of a prober unit for testing circuits of semiconductor chips on a semiconductor wafer in the manufacturing process of electronic devices including LSI. More particularly, the present invention relates to a probe structure of a prober apparatus for use in a probing test. In the probing test, circuit terminals (pads) arranged on the semiconductor chips on a wafer are made to contact with vertical probes for collective measurement of electrical conductivity of the semiconductor chips.
2. Description of the Prior Art
As the semiconductor technology advances, electronic devices have become more highly integrated and a circuit wiring area has increased in each wafer chip. Pads on each wafer chip have also increased in number, and have become more precisely arranged, whereby pad areas become smaller and pad pitches becomes narrower. The pad pitch will become as narrow as 20 μm in the near future.
Chip size packaging (CSP) becomes dominant in which a bear, non-packaged chip is mounted on a circuit board or other substrate. In fabricating the CSP, characteristics and quality of the chips should be verified at the wafer level.
In an exemplary inspection process, a contact assembly is disposed between test equipment and pads on semiconductor chips. The contact assembly includes needle probes arranged in areas each having a portion elastically deformable due to external force. A printed circuit board called probe card is used for electrically connecting the contact assembly and test circuits on the semiconductor chips.
Problems involved in precise and narrow-pitched pad arrangements include the need to provide a compact and dense probe, which abuts a pad on a semiconductor chip for electrical conduction, to correspond to the precise pad arrangements. Problems involved in decreased pad areas include the need of precisely (e.g., to several micrometers) controlling the behavior including scrub operation described later. As semiconductor chips become more sophisticated, there is also a demand for a probe to be applicable to inspections of high speed signals.
A pad on an IC chip to be inspected is typically formed from an aluminum alloy film or gold plating. The surface of the pad is covered with, for example, an oxide film. When the probe tip is made to contact the pad, the tip of the probe pin is vertically pressed (i.e., overdriven) for a certain amount after it touches the pad. The tip rubs (scrubs) a pad surface in a horizontal direction to destroy the oxide film or the like and provide secure conduction between the probe and the pad.
FIG. 7A illustrates a conventional cantilever probe structure. The tip of the probe is kept in a vertical position until it touches the pad on a semiconductor chip. As shown in FIG. 7A, a tip of a vertical probe 102 attached to one end of a cantilever 101 having a length L vertically faces with an upper surface of a pad 103 on a semiconductor chip. The other end of the cantilever 101 is fastened to a fixed portion 104 and the cantilever 101 is kept in a horizontal state. The tip of the vertical probe 102 and the upper surface of the pad 103 are brought into contact for inspection when the pad 103 is moved upward or when the fixed portion 104 is moved downward. The cantilever 101 having the length L rotates about a position of one third of the length L (⅓L) from the fixed portion 104 as a center of rotation. Thus, the tip of the vertical probe 102 is moved largely by the distance do while contacting the upper surface of the pad 103. As a result, especially in a fine pad a small cantilever with small L, the distance of the vertical probe tip to travel with respect to the pad area becomes significantly large, and sometimes the probe tip comes off of the pad 103. Thus, measurement cannot be continued. Pressing force at the vertical probe tip becomes large and the upper surface of the pad 103 is sometimes chipped or damaged. As a result, yield of post processes such as wire bonding may decrease.
In a conventional cantilever probe structure, there exists a tradeoff between an overdrive amount and an amount of horizontal displacement of the tip or a scrubbing amount. That is, a relatively large amount of overdrive is required for absorbing varying vertical dimension of the probe to ensure proper pressing force which causes no damage to the pad and proper pressing force larger than a certain amount at a time on multiple pads. To provide a large amount of overdrive, length L of the beam must be large, which in turn produces a large-sized device.
On the other hand, if the length L of the beam is made small to produce a compact device, the distance of the vertical probe tip to travel with respect to the pad area becomes significantly large, and sometimes the probe tip comes off of the pad 103. Thus, measurement cannot be continued. Pressing force at the vertical probe tip becomes large and the upper surface of the pad is sometimes chipped or damaged.
To meet the above-described requirements for the probe structure, i.e., precise and narrow-pitched pad arrangements, and for precise control of the behavior of the probe near the contact including overdrive and scrubbing function, the present inventors have made the following proposals.
Conventional examples proposed by the present inventors will be described with reference to FIG. 7B.
In order to overcome drawbacks of a conventional cantilever probe structure, a structure of a cantilever 101 is formed as a link structure of a parallel spring 105, and a vertical probe 106 is provided at an end of the parallel spring 105 as shown in FIG. 7B. In this link structure, even if the same vertical contact load as FIG. 7A is acted on the vertical probe 106, since it has a link structure, an amount of displacement d1 of a tip of the vertical probe 106 is set to d1<d0. Thus, the amount of displacement can be significantly small.
A parallel spring herein indicates a plurality of substantially identically shaped beams disposed in parallel with one another. Both ends of the beams are fixed on shared non-deforming supports. One of the supports is moved to cause the beams to move in parallel with one another within a certain range while the other of the supports is fixed.
FIG. 8 illustrates a conventional example with a parallel spring structure. An example is disclosed in the following document.
Patent Document 1: Japanese Patent Application Laid-Open No. 2000-338133
FIG. 8 illustrates a probe 111, a vertical probe portion 112, a fixed portion 113, horizontal beams 114a to 114d, slits 115a to 115c, and a probe tip 116.
The probe 111 is made from a thin elastic metal plate, and consists of the vertical probe portion 112, the fixed portion 113 and four horizontal beams 114a to 114d. The vertical probe portion 112 faces with the pad 103. The probe tip 116 is sharply tapered. The fixed portion 113 is supported by an external support means (not shown). The horizontal beams 114a to 114d have almost identical cross sections. The slits 115a to 115c are provided to define the horizontal beams 114a to 114d separately from a thin plate.
Such a configuration can be obtained by decreased distance from a neutral plane at which the maximum bending stress is generated, i.e., by narrow widths of the beams in order to provide proper spring constant under limited stress. The above configuration is provided to address problems that, when a proper spring constant is to be obtained by one or a few connecting beams, the beams must become longer, which may cause the device size growing.
In addition to the parallel spring structure, the inventors have also proposed a probe which includes a rotationally deformed section connected in series to the parallel spring structure and spring-deformable in the rotational direction in order to ensure scrubbing function. This will be described with reference to FIG. 9.
In FIG. 9A, a probe is formed as a link structure with a parallel spring 200. One end 203 of the parallel spring 200 is a fixed end. A rotationally deformed section 205 having a center of rotation 204 is connected in series to a vertical probe portion 202 of the parallel spring 200. When one end of the rotationally deformed section 205 is brought into contact with a surface of a pad 206, electrical conduction is established between the probe and the pad.
In FIG. 9A, parallel beams 201a and 201b of the probe are kept substantially horizontal until the pad 206 moves vertically and touches the tip of the vertical probe 202. Then, as shown in FIG. 9B, after the pad 206 is brought into contact with the tip of the vertical probe 202 and overdrive is provided to vertically lift the tip in a certain amount, the two parallel beams 201a and 201b of the probe rotate substantially in parallel, followed by vertical movement of the vertical probe 202. At this time, as the vertical probe 202 moves vertically, it inclines slightly by θ due to rotation as shown in FIG. 9B. The tip of the vertical probe 202 moves by distance d1 horizontally.
The rotationally deformed section 205 follows the movement of the vertical probe 202 to move vertically and horizontally. At the same time, the rotationally deformed section 205 begins rotation clockwise about the center of rotation 204 as the overdrive is continuously provided. Operation of the rotationally deformed section at this time will be described in detail with reference to FIG. 10.
FIG. 10 illustrates the loci of center line of the rotationally deformed section near the pad contact portion at three stages as the overdrive is continuously provided. Here, operation of the parallel spring portion is not illustrated and is considered as fixed.
In FIG. 10, reference numeral 222 denotes apart of the probe tip near the contact portion with the pad surface 221, and 223 denotes the center line of the rotationally deformed section. FIG. 10(a) illustrates the state in which the probe tip is just brought into contact with the pad 221. The probe tip 222 is in contact with the pad 221 at a position 222a. After the overdrive is continuously provided advances and the pad 221 pushes the probe 222 up to the state of FIG. 10(b), rotation is added to the tip portion of the rotationally deformed section about the center of rotation 224. Thus, the contact point of the probe tip and the pad is shifted from 222a to 222b. After the overdrive is further provided and the pad 221 pushes the probe 222 up to the state of FIG. 10(c), further rotation is given to the rotationally deformed section and the contact point of the probe tip and the pad is shifted from 222b to 222c. At this time, the center of rotation is shifted from 224a to 224b, and to 224c as the overdrive is further provided. Although not shown in the drawing, the tip of the parallel spring portion also displaced in addition to the above-described shifts.
In this series of operation, relative displacement occurs between the pad surface 221 and the probe tip 222 due to rubbing (scrubbing) operation. When the probe tip and the pad are brought into contact, an oxide film is removed as the contact point is shifted from 222a to 222b, for example. An advantageous effect is provided that, in the second half of the contact, electrical conduction is established during the shift from 222b to 222c. 
As described above, with the probe structure having multiple parallel springs instead of a conventional cantilever structure, a relatively large amount of overdrive is provided even in a small area. Further, the horizontal behavior near the contact portion of the pad and the probe can be precisely controlled. By connecting the rotationally deformed section to the end portion of the parallel spring structure, a structure to precisely control the scrubbing amount is obtained.
However, if the rotationally deformed section is provided at the vertical probe tip of the parallel spring structure in FIG. 9, and when the probe is to be made compact, the horizontal behavior and rotation of the rotationally deformed section also depend on the horizontal displacement of the vertical probe tip. Thus, a problem may be created that precise control of the behavior in the horizontal direction near the contact portion of the pad and the probe is prevented.
In addition, there arises a problem that, with the plural horizontal beams arranged closely, electric capacity becomes large and thus chips with high-speed and high-capacity signals cannot be inspected.
The invention has been devised to solve the above-identified problems. An object of the invention is to provide a probe in which behavior of the probe near a contact including overdrive and scrubbing function can be precisely controlled even in a compact parallel spring probe, by separating a function of a parallel spring structural part which mainly moves vertically from a function of a rotationally deformed section which mainly moves horizontally.
Another object of the invention is to provide a probe with small electric capacity which can be used for inspection of chips having high-speed and high-capacity signals.